Method and apparatus for suppressing the noise of a fan-jet engine

ABSTRACT

A tubular housing is disposed in spaced relation around the casing of a fan-jet engine and extends rearwardly therefrom. A convoluted ring is joined at its circular forward edge to the aft edge of the engine casing and is formed with lobes which extend axially thereof and increase in radial dimension in the downstream direction, so that the aft ends of the lobes project both radially inwardly from said engine casing and radially outwardly to the wall of said housing at the aft end of the latter. The forward edge of a nozzle is joined to the aft edge of the housing, and fan air of the engine flows through the space between the engine casing and the housing, through the spaces between the lobes, and into the nozzle. Exhaust gas of the engine flows from the engine into the passages bounded by the inner surfaces of the lobes and thence into the nozzle.

United States Patent is 3,655,009 Hilbig [451 Apr. 11, 1972 [54] METHODAND APPARATUS FOR 3,262,264 7/1966 Gardiner et al ..239/127.3SUPPRESSING THE NOISE ()F A FAN. 3,390,837 7/1968 Freeman ..239/265.17JET I E I 3,432,100 3/1969 Hardy et al. ..239/l27.3 7 3,463,402 8/1969Langston ..181/33 HC [72] Inventor: Jack H. Hilbig, Chula Vista, Calif.3,527,317 9/ 1970 Motsinger ..239/127.3 [73] Assignee: Rohr Corporation,Chula Vista, San Primary Examiner Robert S. ward Jr Dlego, Cahf-Attorney-George E. Pearson 22 F'] (1: Se I. 18 1969 21 A 1 N 85: 070[57] ABSTRACT I 1 0" A tubular housing is disposed in spaced relationaround the casing of a fan-jet engine and extends rearwardly therefrom.A [52] U.S. Cl ..181/33 HC, 181/51, 239/ 1 27.3, convoluted ring isjoined at its circular forward edge to the aft 239/265.17 edge of theengine casing and is formed with lobes which ex- [51] lnt.Cl ..B64d33/06, F01n 1/14 tend axially thereof and increase in radial dimensionin the [58} Field of Search 181/43, 51, 33, 33.22, 33.221, downstreamdirection, so that the aft ends of the lobes project18l/33.222;239/127.3, 265.11, 265.13, 265.17 both radially inwardly fromsaid engine casing and radially outwardly to the wall of said housing atthe aft end of the 56] References Cited latter. The forward edge of anozzle is joined to the aft edge of the housing, and fan air of theengine flows through the space UNITED STATES PATENTS between the enginecasing and the housing, through the spaces between the lobes, and intothe nozzle. Exhaust gas of the en- 2426'833 9/1947 Lloyd 181/33 HC gineflows from the engine into the passages bounded by the 3,027,710 4/ 1962Maymer 181/33 HC inner surfaces of the lobes and thence into the nozzle.3,053,340 9/1962 Kutney ...l8l/33 HC 3,174,581 3/1965 Duthion et a1..181/33 11C 2 Claims, 2 Drawing Figures i 1, l8 -r l s I -r' r I "P 1%l l i Q I v 36v es il i I l :2 I I I i 24 I 'r I 22 r x20 a l r I l I )iI'ZZU 36 PATENTEDAPR 1 1 m2 INVENTOR. JACK H. HILBIG I I I .ll

BY Q

AT TORN E Y METHOD AND APPARATUS FOR SUPPRESSING THE NOISE OF A FAN-JETENGINE SUMMARY OF THE INVENTION This invention relates to jet-propelledaircraft and more particularly to a method and apparatus for reducingthe noise created by aircraft having engines of the fan-jet type.

Part of the noise associated with the operation of jetpropelled aircraftresults from the flow through the atmosphere of the high velocityexhaust gas discharged from the engine, or engines, of such aircraft.The amount of sound energy generated by streams of exhaust gas dependsupon the temperature and velocity thereof. The present inventionprovides for the mixing of the high velocity, high temperature primaryjet stream of a fan-jet engine with the relatively low velocity, lowtemperature fan air of said engine, which mixing is effected by aconvoluted ring disposed between the aft end of the engine casing and athrust nozzle associated therewith. The combined jet stream of exhaustgas and fan air which is discharged from the nozzle has a lower velocitythan that of the exhaust gas when the latter is discharged as a separatestream, and the noise generated by passage of the combined jet streamthrough the atmosphere is thus less than that which is generated whenthe exhaust gas and fan air are discharged as separate streams. Thecombined jet stream also has a lower temperature than that of theexhaust gas, which further reduces the noise generated downstream fromthe propulsion assembly.

In the preferred embodiment of the invention a tubular housing isdisposed in spaced relation around a fan-jet engine casing and projectsrearwardly therefrom. A thrust nozzle is secured to the aft end of thehousing, and a tube is mounted on the aft bearing housing of the enginedrive shaft and extends to a point radially aligned with the junction ofthe housing and the thrust nozzle, the aft end of this tube supporting acone, or plug, which extends into the forward portion of the throat ofthe thrust nozzle. A convoluted ring is joined at its circular forwardedge to the aft edge of the engine casing, this ring being formed with aplurality of lobes which extend radially thereof and gradually increasein radial dimension in the downstream direction so that their aft endsproject both radially inwardly from the engine casing and radiallyoutwardly to the wall of the housing at the point where the nozzle isjoined to the latter. Fan air of the engine passes through the spacebetween the engine casing and the housing, and thence through the spacesbetween the lobes of the ring into the nozzle, while exhaust gas passesfrom the engine into the ring and flows through the lobes of the latterinto the nozzle. Hence streams of fan air and streams of exhaust gasenter the nozzle in alternately disposed relation, each of said streamsextending radially from the aforesaid cone at the aft end of the ring tothe wall of the nozzle. These fan air and exhaust gas streams mixtogether in the nozzle and thus suppress the noise of operation of thejet engine assembly as described hereinbefore.

DESCRIPTION OF THE DRAWINGS FIG. 1 is a side elevation of a preferredembodiment of this invention, the drawing illustrating in solid linesthe rear portion of a housing which envelops a fan-jet engine and athrust nozzle attached to the aft end of said engine, and illustratingin broken lines components which are disposed within said housing andnozzle; and

FIG. 2 is a rear view of the same embodiment.

DETAILED DESCRIPTION As illustrated in FIG. 1, a preferred embodiment ofthe present invention comprises a tubular housing, or nacelle, which isgenerally designated by the number and which is formed of a forwardsection 12 and an aft section 14 attached by suitable means to saidforward section. Disposed within housing 10 is a jet engine the turbinecasing 16 of which is il lustrated in the drawing by broken lines. Thehousing is concentric with casing 16, and the space therebetween isconnected with the fan section of the engine by means of ducts (notshown) so that it serves as a passage for the flow of fan air(represented by single-headed arrows in the drawings) to afrusto-conical thrust nozzle 18 mounted on the aft end of said housing.A tube 20 is fixedly attached to the aft bearing housing 22 of the driveshaft (not shown) of the engine, said tube extending rearwardly fromsaid bearing housing in coaxial relation with housing 10 and terminatingat the plane which includes the aft edge of the latter (which plane isperpendicular to the longitudinal axis of the housing). the base of acone 24 is secured to the aft edge of tube 20, and the cone thusprojects into the throat of nozzle 18.

The forward, circular edge of a convoluted ring, generally designated bythe number 26, is fixedly joined to the aft edge 28 of casing 16, thisring being formed with a plurality of lobes 30 which are shown in endview in FIG. 2. The lobes gradually increase in radial dimension in thedownstream direction, so that at the forward portion of the ring thevalleys 32 between the lobes are shallow, whereas at the aft end of thering said valleys are deep. Furthermore, the construction of the ring issuch that its lobes project both radially inwardly and radiallyoutwardly from the aft edge of casing 16 (as illustrated by the brokenlines designated 34, 36 in FIG. 1), and the aft end of the lobes arefixedly secured by suitable means to the aft end of tube 20 and to thewall of housing 10 at the junction of the latter and nozzle 18. Theconvoluted aft edge of the ring lies in the plane which includes the aftedge of housing 10 and the aft edge of tube 20.

OPERATION As illustrated by double headed arrows in FIG. 1, exhaust gasof the engine within housing 10 is discharged into the forward,cylindrical end of ring 26 and is divided into separate streams whichrespectively flow through the passages 38 (see FIG. 2) bounded by theinner surfaces of lobes 30 of the ring. Thus streams of exhaust gasenter the throat of nozzle 18 in circumferentially spaced relation toone another, and these streams extend radially from cone 24 to the wallof the nozzle. Fan air (represented by single-headed arrows, aspreviously noted) flows through the spaces between lobes 30 and enterthe nozzle in separate streams which are disposed in alternate relationbetween the aforedescribed streams of exhaust gas, said streams of fanair also extending radially from cone 24 to the wall of the nozzle. InFIG. 2 double-headed arrows indicate the flow of a portion of theexhaust gas outwardly toward the wall of housing 10 after said gas isdischarged from the engine, and single-headed arrows indicate the flowof a portion of the fan air inwardly toward tube 20 after said fan airis discharged from the space between housing 10 and casing 16.

It will be clear from the foregoing description of one embodiment of theinvention that the convoluted ring 26 causes exhaust gas and fan air toflow into the nozzle associated therewith in a manner which results inthorough mixing of said gas and air inside the nozzle, thus causing thenoise which is generated by the combined jet stream discharged from saidnozzle to be less than the noise which would be generated if the exhaustgas and fan air were permitted to flow through the atmosphere inseparate streams. It will also be recognized that various changes andmodifications could be made in the described and illustrated apparatuswithout departing from the concept of the invention. For example, insome embodiments of the invention tube 20'and cone 24 can be omittedwithout materially affecting the operation of the apparatus. Hence thescope of the invention should be considered to be limited only by theterms of the claims appended thereto.

What is claimed as new and useful and desired to be secured by US.Letters Patent is:

1. In a jet propulsion plane having a fan-jet engine, the combinationcomprising:

a tubular housing disposed in spaced relation around the aft portion ofthe casing of said engine and projecting beyond,

the aft edge thereof, fan air of said engine flowing through the spacebetween said housing and said casing;

a convoluted ring the forward edge of which is fixedly joined to the aftedge of said casing, said ring being formed with lobes which extendaxially thereof and gradually increase the radial dimension in thedownstream direction so that their aft ends project both radiallyinwardly and radially outwardly from the aft edge of said casing, saidlobes abutting the wall of said housing at the aft end of the latter;and

a thrust nozzle the forward edge of which is fixedly joined to the aftedge of said housing, fan air of said engine flowing from the spacebetween said housing and said casing into the spaces between the lobesof said ring and thence dividing therein for flow into said nozzle, theaft ends of the lobes of said ring being fixedly joined together so thatexhaust gas of said engine flowing through the radially projectingpassages bounded by the inner surfaces of said lobes and thence dividingtherein for flow into said nozzle, whereby alternately disposed streamsof fan air and exhaust gas enter the forward end of said nozzle.

2. The combination defined in claim 1 including:

a tube fixedly connected to the aft bearing housing of the drive shaftof said engine and extending rearwardly therefrom in coaxial relationwith said housing, the aft ends of the lobes of said ring being fixedlyjoined to the aft end of said tube; and

a cone the base edge of which is fixedly joined to the aft edge of saidtube.

1. In a jet propulsion plane having a fan-jet engine, the combinationcomprising: a tubular housing disposed in spaced relation around the aftportion of the casing of said engine and projecting beyond the aft edgethereof, fan air of said engine flowing through the space between saidhousing and said casing; a convoluted ring the forward edge of which isfixedly joined to the aft edge of said casing, said ring being formedwith lobes which extend axially thereof and gradually increase theradial dimension in the downstream direction so that their aft endsproject both radially inwardly and radially outwardly from the aft edgeof said casing, said lobes abutting the wall of said housing at the aftend of the latter; and a thrust nozzle the forward edge of which isfixedly joined to the aft edge of said housing, fan air of said engineflowing from the space between said housing and said casing into thespaces between the lobes of said ring and thence dividing therein forflow into said nozzle, the aft ends of the lobes of said ring beingfixedly joined together so that exhaust gas of said engine flowingthrough the radially projecting passages bounded by the inner surfacesof said lobes and thence dividing therein for flow into said nozzle,whereby alternately disposed streams of fan air and exhaust gas enterthe forward end of said nozzle.
 2. The combination defined in claim 1including: a tube fixedly connected to the aft bearing housing of thedrive shaft of said engine and extending rearwardly therefrom in coaxialrelation with said housing, the aft ends of the lobes of said ring beingfixedly joined to the aft end of said tube; and a cone the base edge ofwhich is fixedly joined to the aft edge of said tube.